The present invention relates to the technical field of medical aerosol generator systems.
The purpose of medical aerosol generator systems is to convert a medicated liquid or powder into aerosol form so that it can be administered to the airways of the respiratory tract.
There are various commercially available medical aerosol generator systems in the form of pneumatically controlled, ultrasonic and vibrating-membrane devices in particular, as well as pressurised canisters with a metering valve.
The Applicant is one of the leading firms that manufacture and market this type of device. Despite all the research efforts devoted to these devices (generators, nebulisers and pressurised canisters), the various published studies on this subject all agree and confirm that a large proportion of the dispensed aerosol is lost and wasted rather than being used for the desired therapeutic treatment. Authors and manufacturers alike estimate the proportion of aerosol that is actually used at approximately 25% (inhalable or available fraction). Losses are due to several parameters, including loss of the medication in the atmosphere when the patient exhales, the mass of medication lost in the nebuliser at the end of nebulisation and the mass lost during transfer of the aerosol. The design of devices with outlet vents is one explanation with the particles naturally escaping into the open air.
Inhaler chambers, for example in the case of pressurized canisters with a valve, are one means of limiting losses.
In this case, transfer of the aerosol essentially takes place in a container which is horizontal when the device is placed in/over the mouth so that the sprayed aerosol, the particle size distribution of which is highly variable and heterogeneous, partially fills the space in question. Thus, it is readily obvious that the larger sized particles tend to drop very quickly into the bottom of the horizontal container well before inhalation simply due to the effect of gravity. It is thus readily obvious that there is a fine layer of medicated particles that are not inhaled.
Some other devices, especially those with a vibrating membrane, make it possible to spray all the aerosol into a small vertical chamber but the lower part of this chamber forming a container is likely to receive medicated particles at high speed which causes impaction and therefore loss of medicated particles on the walls of the chamber. In any case and according to tests that have been performed, even in this type of device, active use of the dispensed aerosol is 25% of the volume introduced into the generator system on average.
According to the prior art as defined in the example in U.S. Pat. No. 5,596,982 and WO 03/089036, the aerosol generators use turbulence or vortex effects during transport of the aerosol and these are the cause of loss of aerosol particles. Obtaining this turbulence effect requires entry of air to take place in a plane that is perpendicular to the transport axis of the aerosol.
The objective of the invention is to reduce the loss of aerosols.
The Applicant's approach was therefore to rethink the problem of this partial use of the aerosol and to attempt to find a solution in order to improve the conditions for therapeutic treatment of patients.
Various possibilities were examined by reducing or eliminating the vent(s) or opening(s) on the nebuliser or introducing an additional blower system in order to increase the circulation of medicated aerosol through the horizontal transfer chamber to the area where the aerosol is inhaled by mouth.
In practice, it was impossible to adopt these solutions because they only partially solved the problem in question as they only improved the proportion of inhaled aerosol insignificantly.